Standard Test Method for High-Strain Dynamic Testing of ...

1 Designation: D 4945 08 Standard Test Method forHigh-Strain Dynamic Testing of Deep Foundations1 This Standard is issued under the fixed designation D 4945; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon ( ) indicates an editorial change since the last revision or Scope* This Dynamic test Method covers the procedure forapplying an axial impact force with a pile driving hammer ora large drop weight that will cause a relatively high strain at thetop of an individual vertical or inclined deep foundation unit,and for measuring the subsequent force and velocity responseof that deep foundation unit. High-Strain Dynamic testingapplies to any deep foundation unit, also referred to herein asa pile, which functions in a manner similar to a driven pile ora cast-in-place pile regardless of the Method of installation, andwhich conforms with the requirements of this test This Standard provides minimum requirements for dy-namic Testing of deep foundations.

2 Plans, specifications, orprovisions (or combinations thereof) prepared by a qualifiedengineer may provide additional requirements and proceduresas needed to satisfy the objectives of a particular test engineer in responsible charge of the foundation design,referred to herein as the Engineer , shall approve any devia-tions, deletions, or additions to the requirements of The proper conduct and evaluation of High-Strain dy-namic tests requires special knowledge and experience. Aqualified engineer should directly supervise the acquisition offield data and the interpretation of the test results so as topredict the actual performance and adequacy of deep founda-tions used in the constructed foundation. A qualified engineershall approve the apparatus used for applying the impact force,driving appurtenances, test rigging, hoist equipment, supportframes, templates, and test The text of this Standard references notes and footnoteswhich provide explanatory material.

3 These notes and footnotes(excluding those in tables and figures) shall not be consideredas requirements of the Standard . The word shall indicates amandatory provision, and the word should indicates arecommended or advisory provision. Imperative sentencesindicate mandatory The values stated in SI units are to be regarded asstandard. No other units of measurement are included in All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPracticeD The Method used to specify how data are collected,calculated, or recorded in this Standard is not directly related tothe accuracy to which the data can be applied in design or otheruses, or both. How one applies the results obtained using thisstandard is beyond its Standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this Standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to a specificprecautionary statement, seeNote Referenced standards :2C 469 Test Method for Static Modulus of Elasticity andPoisson s Ratio of Concrete in CompressionD 198 Test methods of Static tests of Lumber in StructuralSizesD 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 1143/D 1143 MTest methods for Deep Foundations Un-der Static Axial Compressive LoadD 3689 Test methods for Deep Foundations Under StaticAxial Tensile LoadD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD 6026 Practice for Using Significant Digits in Geotechni-cal Data3.

4 For common definitions of terms used inthis Standard , see TerminologyD of Terms Specific to This in-place pile,n a deep foundation unit made ofcement grout or concrete and constructed in its final location,1 This test Method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee on Deep edition approved Oct. 1, 2008. Published November 2008. Originallyapproved in 1989. Last previous edition approved in 2000 as D 4945 referenced ASTM standards , visit the ASTM website, , orcontact ASTM Customer Service at ForAnnual Book of ASTMS tandardsvolume information, refer to the Standard s Document Summary page onthe ASTM *A Summary of Changes section appears at the end of this example, drilled shafts, bored piles, caissons, auger castpiles, pressure-injected footings, foundation,n a relatively slender structuralelement that transmits some or all of the load it supports to thesoil or rock well below the ground surface, that is, a drivenpile, a cast-in-place pile, or an alternate structural elementhaving a similar foundation cushion,n the material insertedbetween the helmet on top of the deep foundation and the deepfoundation (usually plywood).

5 Foundation impedance,n a measure of the deepfoundation s resistance to motion when subjected to an impactevent. Deep foundation impedance can be calculated bymultiplying the cross-sectional area by the Dynamic modulus ofelasticity and dividing the product by the wave speed. Alter-natively, the impedance can be calculated by multiplying themass density by the wave speed and cross-sectional ~EA/c!5rcA(1)where:Z= impedance,E= Dynamic modulus of elasticity,A= cross-sectional area,c= wave speed, andr= mass pile,n a deep foundation unit made of pre-formed material with a predetermined shape and size andtypically installed by impact hammering, vibrating, or ,n a structural section placed between theimpact device and the deep foundation during installation cushion,n the material inserted between thehammer striker plate and the helmet on top of the event,n the period of time during which thedeep foundation is moving due to the impact force force,n in the case of strain transducers, theimpact force is obtained by multiplying the measured strain ( )with the cross-sectional area (A) and the Dynamic modulus ofelasticity (E).

6 ,n a stiff structural member placed inside athin shell to allow impact installation of the thin section of impact,n the first time after the start ofthe impact event when the acceleration is zero. SeeFig. velocity,n the instantaneous velocity of aparticle in the deep foundation as a strain wave passes , n or v the redriving of a previously drivenpile, typically after a waiting period of 15 min to 30 days ormore, to assess changes in ultimate axial compressive staticcapacity during the time elapsed after the initial speed,n the speed with which a strain wavepropagates through a deep foundation. It is a property of thedeep foundation composition and for one-dimensional wavepropagation is equal to the square root of the quotient of theModulus of Elasticity divided by mass density:c=(E/r)1 Significance and Based on the measurements from strain or force, andacceleration, velocity, or displacement transducers, this testmethod obtains the force and velocity induced in a pile duringan axial impact event (seeFigs.)

7 1 and 2). The Engineer mayanalyze the acquired data using engineering principles andjudgment to evaluate the integrity of the pile, the performanceof the impact system, and the maximum compressive andtensile stresses occurring in the If sufficient axial movement occurs during the impactevent, and after assessing the resulting Dynamic soil responsealong the side and bottom of the pile, the Engineer may analyzeFIG. 1 Typical Force and Velocity Traces Generated by the Apparatus for Obtaining Dynamic MeasurementsD4945 082the results of a High-Strain Dynamic test to estimate the ultimateaxial static compression capacity (seeNote 1). Factors thatmay affect the axial static capacity estimated from dynamictests include, but are not limited to the:(1)pile installationequipment and procedures,(2)elapsed time since initialinstallation,(3)pile material properties and dimensions,(4)type, density, strength, stratification, and saturation of the soil,or rock, or both adjacent to and beneath the pile,(5)quality ortype of Dynamic test data,(6)foundation settlement,(7)analysis Method , and(8)engineering judgment and the Engineer does not have adequate previous experiencewith these factors, and with the analysis of Dynamic test data,then a static load test carried out according to Test MethodD 1143 should be used to verify estimates of static capacity andits distribution along the pile length.

8 Test Method D 1143provides a direct and more reliable measurement of The analysis of a Dynamic test will under predict the ultimateaxial static compression capacity if the pile movement during the impactevent is too small. The Engineer should determine how the size and shapeof the pile, and the properties of the soil or rock beneath and adjacent tothe pile, affect the amount of movement required to fully mobilize thestatic capacity. A permanent net penetration of as little as 2 mm per impactmay indicate that sufficient movement has occurred during the impactevent to fully mobilize the capacity. However, high displacement drivenpiles may require greater movement to avoid under predicting the staticcapacity, and cast-in-place piles often require a larger cumulative perma-nent net penetration for a series of test blows to fully mobilize thecapacity. Static capacity may also decrease or increase over time after thepile installation, and both static and Dynamic tests represent the capacityat the time of the respective test.

9 Correlations between measured ultimateaxial static compression capacity and Dynamic test estimates generallyimprove when using Dynamic restrike tests that account for soil strengthchanges with time ( ).NOTE2 Although interpretation of the Dynamic test analysis mayprovide an estimate of the pile s tension (uplift) capacity, users of thisstandard are cautioned to interpret conservatively the side resistanceestimated from analysis of a single Dynamic measurement location, and toavoid tension capacity estimates altogether for piles with less than 10 membedded length. (Additional transducers embedded near the pile toe mayalso help improve tension capacity estimates.) If the Engineer does nothave adequate previous experience for the specific site and pile type withthe analysis of Dynamic test data for tension capacity, then a static load testcarried out according to Test MethodD 3689should be used to verifytension capacity estimates.

10 Test MethodD 3689provides a direct andmore reliable measurement of static tension The quality of the result produced by this test Method isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of PracticeD 3740are generally considered capable of competentand objective Testing /sampling/inspection/etc. Users of this test methodare cautioned that compliance with PracticeD 3740does not in itselfassure reliable results. Reliable results depend on many factors; PracticeD 3740provides a means of evaluating some of those Device A High-Strain Dynamic test measuresthe pile response to an impact force applied at the pile head andin concentric alignment with its long axis (seeFigs. 2 and 3).The device used to apply the impact force should providesufficient energy to cause pile penetration during the impactevent adequate to mobilize the desired capacity, generallyproducing a maximum impact force of the same order ofmagnitude, or greater than, the ultimate pile capacity (staticplus Dynamic ).